Abstract
Fermi-Dirac distribution for doped semiconductors and Burstein-Moss effect have been correlated first time to figure out the conductivity type of ZnO. Hall Effect in the Van der Pauw configuration has been applied to reconcile our theoretical estimations which evince our assumption. Band-gap narrowing has been found in all p-type samples, whereas blue Burstein-Moss shift has been recorded in the n-type films. Atomic Force Microscopic (AFM) analysis shows that both p-type and n-type films have almost same granular-like structure with minor change in average grain size (∼ 6 nm to 10 nm) and surface roughness rms value 3 nm for thickness ∼315 nm which points that grain size and surface roughness did not play any significant role in order to modulate the conductivity type of ZnO. X-ray diffraction (XRD), Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS) have been employed to perform the structural, chemical and elemental analysis. Hexagonal wurtzite structure has been observed in all samples. The introduction of nitrogen reduces the crystallinity of host lattice. 97% transmittance in the visible range with 1.4 × 107 Ω-1cm-1 optical conductivity have been detected. High absorption value in the ultra-violet (UV) region reveals that NZOs thin films can be used to fabricate next-generation high-performance UV detectors.
Highlights
Zinc oxide (ZnO) is a versatile semiconductor with a wide band gap of 3.37 eV at room temperature (RT), having excellent piezoelectric[1] and optoelectronics[2] properties to utilize for industrial applications.[3]
ZnO (99.999% purity) target of diameter 3" and 0.125" thickness has been used for sputtering at room temperature on glass substrates. 99.99% pure Nitrogen has been added to the chamber during growth process in order to dope with ZnO with specific and controlled amount
At high N-doping, crystalline phase tends to shift towards amorphous behavior which emphasizes that high level of N-doping provides more lattice mismatches which disturb the original crystalline behavior of ZnO films.[28]
Summary
This modified shape of conduction band has a vital role in the shift of optical transitions. Previous reports described that the origin of band renormalization is the non-parabolic shape of the conduction band of host lattice, which further can be enhanced by the addition of impurity doping. As in the impurity doping, the hybridization of electronic states with the conduction states causes to enhance the renormalization effect of band gap energy.[9] In the present study, we correlated the Fermi-Dirac distribution for doped semiconductor and Burstein-Moss effect in order to estimate conductivity type of ZnO: N thin films which further reconciled via Hall measurements. The state of the art RF magnetron sputtering system has been used to prepare ZnO: N thin films on the glass substrate at room temperature
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